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        * {
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        div {
            width: 300px;
            height: 300px;
            background-color: pink;
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        /* 1:物理像素 就是我们说的分辨率 iphone8的物理像素是750 */
        /* 2：在iphone8里面 1px 开发像素 = 2个物理像素 */
        
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